The regulation of DNA synthesis and cell division will be studied by exposing populations of bacteria to drugs which block steps in the synthesis of DNA and cell division at particular stages in these processes. A large number of heat sensitive and cold sensitive mutants unable to carry out normal DNA synthesis and cell division will be isolated, characterized and mapped genetically in order to find out how many genes are essential to carry out the normal processes, in what order their products are required during the divison cycle of the cell, the site and mode of action of the gene products and their biochemical nature. The relationship between DNA synthesis and cell division will be explored by drugs or mutants which block one process and interfere secondarily with the other and by establishing the existence of physical connections between replicating DNA and cell wall or membrane. The rates of chromosome-changing events like gene duplication, deletion, crossing over and point mutations will be measured. A detailed and intensive map particularly of temperature sensitive mutants of the bacterial chromosome will be made for studying these chromosome changes and the consequences of them for bacterial evolution. In addition to the conventional genetic, biophysical, and biochemical methods used in molecular biology we will take advantage of automatic techniques recently developed in our laboratory for measuring the size and characterizing the morphology of very large numbers of bacterial colonies.